GB2315851A

GB2315851A - Vehicle headlight

Info

Publication number: GB2315851A
Application number: GB9715700A
Authority: GB
Inventors: Hiroyuki Serizawa; Satoshi Yamamura
Original assignee: Koito Manufacturing Co Ltd
Current assignee: Koito Manufacturing Co Ltd
Priority date: 1996-07-25
Filing date: 1997-07-24
Publication date: 1998-02-11
Anticipated expiration: 2017-07-24
Also published as: DE19731977B4; GB2315851B; DE19731977A1; JPH1040710A; US6062714A; GB9715700D0; JP3145927B2

Abstract

A vehicle headlight 10 having a discharge bulb 18, and a reflector 16, the reflector having a first reflecting surface region 22A which is a substantially upper part of the reflecting region 22 with respect to the optical axis of the reflector Ax and which reflects light to form a sub-light distribution pattern (P, Fig. 3) having an oblique cut line (CL1, Fig. 3) and a horizontal cut line (CL2, Fig. 3); and a second reflecting surface region 22B located below the optical axis Ax and which forms a sub light distribution pattern (Pw) nearer the vehicle and with a larger maximum horizontal diffusion angle than the first pattern (P). The cut lines are formed by shades which may be supporting legs 20b1, 20b2 of a mask 20 in front of the bulb or masking strips (18f, 18f2, Fig. 7) on a surface of the bulb.

Description

2315851 VEHICLE HEADLIGHT This invention relates to a vehicle headlight

with a discharge bulb, and more particularly to a sub light distribution pattern forming headlight.

Recently, a discharge lamp has been employed as the light source of a vehicle headlight, because it is able to perform a high brightness irradiation.

In the case where, with a headlight with such a discharge lamp, a sub light distribution pattern having an oblique cut line and a horizontal cut line is formed, the resultant pattern is high in distant recognition, and wide in irradiation angle.

The power of the discharge lamp is great. Hence, the sub light distribution pattern is formed by light reflected from the reflecting surface region of the reflector reflecting surface which is only a substantially upper half thereof with respect to the optical axis of the reflector.

As was described above, the sub light distribution pattern is formed only by the light reflected from the reflecting surface region of the reflector reflecting surface which is a substantially upper half thereof with respect to the optical axis of the reflector. However, the light advancing towards the remaining reflecting surface region is not used at all. This is not economical nor efficient. In addition, in order to improve the traveling safety of a vehicle at night, it is desirable to utilize the output light of the discharge bulb as much as possible.

In view of the foregoing, an object of the invention is to provide a sub light distribution pattern forming vehicle headlight with a discharge bulb which is improved in lamp efficiency and in the driving safety of a vehicle at night.

The foregoing object of the invention has been achieved by the utilization of the lower reflecting surface region of the reflector as a reflecting surface region to reflect a predetermined wide diffusion distribution pattern to complement the sub light distribution pattern.

That is, in a vehicle headlight which comprises a discharge bulb, and a reflector having a reflecting surface adapted to reflect the output light of the discharge bulb forwardly, and for a sub light distribution pattern having an oblique cut line and a horizontal cut line, of the reflecting surface, a first reflecting surface region which is a substantially upper half thereof with respect to the optical axis of the reflector, is so designed as to form the sub light distribution pattern with the aid of light reflected from the reflecting surface region, and of the reflecting surface, a second reflecting surface region which is located below the optical axis of the reflector reflects the output light of the discharge bulb downwardly in a deflection mode and reflect the output light of the discharge bulb horizontally in a diffusion mode, so that light reflected from the reflecting surface region forms in the part of the sub light distribution pattern near a vehicle a wide diffusion sub light distribution pattern which has a horizontal diffusion angle larger than the maximum horizontal diffusion angle of the sub light distribution pattern.

The aforementioned "second reflecting surface region,' is not particularly limited in with, position, and so forth as long as it is possible to form the "wide diffusion distribution pattern". For instance, in the case where a shade is provided near the discharge bulb, the shade comprising a front end portion adapted to intercept light emitted forwardly from the discharge bulb, and a pair of legs through which the front end portion is secured to the reflector, and the upper edges of the pair of legs form the oblique cut line and the horizontal cut line, the second reflecting surface region may be a reflecting surface region which is located between the shades of the pair of legs.

Furthermore, the "second reflecting surface region" may be of a single curved surface; however, the second reflecting surface region may comprise a plurality of reflecting surface elements.

The "second reflecting surface region" is so designed as to downwardly reflect the output light of the discharge bulb in a deflection mode and reflect the output light of the discharge bulb horizontally in a diffusion mode; however, in order to reflect the output light of the discharge bulb downwardly in a deflection mode, the following arrangements may be employed.

That is, the vertical section of the first reflecting surface region is generally parabolic; however, the vertical section of the second reflecting surface region is also made parabolic, and the parabolic axis of the second reflecting surface region may be directed downwardly with respect to the parabolic axis of the first reflecting surface region; and the parabolic axis of the second reflecting surface region may be located below the parabolic axis of the first reflecting surface region; and the parabolic focal length of the second reflecting surface region may be longer than the parabolic focal length of the first reflecting surface region.

As was described above, the first reflecting surface region which is a substantially upper half with respect to the optical axis of the reflector forms the sub light distribution pattern with the aid of light reflected from the first reflecting surface region, and the light reflected from the second reflecting surface region which is located below the optical axis of the reflector forms in a part of the sub light distribution pattern near the vehicle a wide diffusion sub light distribution pattern which has a horizontal diffusion angle larger than the maximum horizontal diffusion angle of the sub light distribution pattern.

Hence, with the sub light distribution pattern is utilized to visually recognize objects in front of the vehicle, and the wide diffusion distribution pattern makes it ready for the driver to find a walker quickly who comes in front of the vehicle from side. That is, the auxiliary function of the sub light distribution pattern is sufficiently performed.

Hence, the sub light distribution pattern forming vehicle headlight with the discharge bulb of the invention is high in lamp efficiency and in the driving safety of the vehicle at night.

In the discharge bulb, metal iodide is deposited on the lower portion of the inner wall of the ball-shaped section which forms the discharge chamber of the discharge bulb. Hence, the light advancing downwardly from the discharge bulb is colored yellow by the metal iodide. Hence, the light reflected from the second reflecting surface region which is located below the optical axis of the reflector is colored yellow. With the yellowish wide diffusion distribution pattern thus formed, in bad weather such as foggy weather and even at night, the front field of vision of the vehicle is sufficiently clear.

If the "second reflecting surface region" is made up of a plurality of reflecting surface elements, then the aforementioned wide diffusion distribution pattern can be formed with ease.

In the accompanying drawings:

FIG. 1 is a front view of a vehicle headlight, which constitutes an embodiment of the invention; FIG. 2 is a sectional side view of the vehicle headlight shown in FIG. 1; FIG. 3 is a screen distribution pattern diagram for a description of the function of the vehicle headlight;

FIG. 4 is a sectional view taken along line IV-IV in FIG. 1; FIG. 5(a) is a diagram corresponding to FIG. 4, showing a concrete example of a reflecting surface, and FIGS. 5(b) and 5(c) are diagrams showing modifications of the reflecting surface shown in FIG. 5(a); FIG. 6 is a perspective view of a discharge bulb in the above-described vehicle headlight; FIG. 7 is a sectional view of a discharge bulb, showing a modification of the above-described embodiment of the invention; FIG. 8 is a front view corresponding to FIG. 1, showing a preferable position of an upper and lower border line in the case where, in the reflecting surface of the reflector of the vehicle headlight, a reflecting surface region forming a sub light distribution pattern is divided into a plurality of segments; and FIG. 9 is a screen distribution pattern diagram for a description of the arrangement of the vehicle headlight shown in FIG. 8.

A preferred embodiment of the invention will be described with reference to the accompanying drawings.

FIG. 1 is a front view of a vehicle headlight, the embodiment of the invention; and FIG. 2 is a sectional side view of the vehicle headlight shown in FIG. 1.

As shown in FIGS. 1 and 2, in the vehicle headlight 10 of the invention, a lens 12 and a body 14 define a space, in which a reflector 16 with a discharge bulb 18 and a shade 20 is provided in such a manner that it is vertically and horizontally tiltable, whereby, as shown in FIG. 3, a sub light distribution pattern P of left distribution type having an oblique cut line (15' cut line) CL1 and a horizontal cut line CL2 is formed.

The aforementioned lens 12 is a plain lens, and the above-described sub light distribution pattern P is formed by the reflector 16.

The reflecting surface 22 of the aforementioned reflector 16 is designed as follows: A paraboloid of revolution with an optical axis Ax extended in a front-to- rear direction is employed as a reference surface. The reference surface is divided into a plurality of segments, to which reflecting surface elements 22s different in curvature from the reference surface are assigned. The curvatures of those reflecting surface elements 22s are set to suitable values, to obtain the above-described sub light distribution pattern P.

In the formation of the sub light distribution pattern P, as shown in FIG. 1, the reflecting surface 22 includes a reflecting surface region 22A which is substantially an upper half thereof with respect to the optical axis AS, and light reflected from this reflecting surface region 22A is utilized (as described later).

The discharge bulb 18 is a metal halide discharge bulb, and its optical axis (reference axis) is the same as the optical axis Ax of the reflector 16. The discharge bulb 18 is mounted on the reflector 16 in such a manner that its light emitting section (arc) 18a is slightly ahead of the focal position F of the paraboloid of revolution which is the reference surface of the reflector 16. In order to turn on the discharge bulb 18, a high voltage is required. Therefore, the discharge bulb 18 is connected through a bulb socket 24 and the high voltage cord 26 to a lighting circuit (not shown). An extension 28 is provided in front of the abovedescribed reflector 16.

The above-described shade 20 comprises: a cupshaped 8- front end portion 20a which covers the front of the discharge bulb 18; a pair of legs 20bl and 20b2 whose rear ends are fixedly secured to the reflector 16. The front end portion 20a intercepts the light beam which advances towards the front of the lamp from the discharge bulb 18, while the pair of legs 20b intercept the light beams which advance to predetermined right and left regions of the reflecting surface 22 of the reflector 16 from the discharge bulb 18.

On the reflecting surface 22 of the reflector, the shades SBl and SB2 of the pair of legs 20bl and 20b2 are formed radially; however, it should be noted that the aforementioned sub light distribution pattern P is formed by light reflected from the reflecting surface region 22A which are located above the pair of shades SB1 and SB2. In this operation, the upper edge of the right leg 20bl forms the aforementioned oblique cut line CL1, while the upper edge of the left leg 20b2 forms the horizontal cut line CL2.

In the reflecting surface region 22B of the reflecting surface 22, which is located below the pair of shades SBl and SB2, the light reflected from the reflecting surface region 22B, as shown in FIG. 3, forms a wide diffusion distribution pattern PW in front of the sub light distribution pattern P which has a horizontal diffusion angle which is larger than the maximum horizontal diffusion angle of the sub light distribution pattern P. The reflecting surface region 22B is formed in the same manner as the above- described reflecting surface region 22A. That is, a predetermined reference surface (which is a paraboloid of revolution which is different in focal length and in focal position from the paraboloid of revolution which is the reference surface of the reflecting surface region 22A) is divided into a plurality of segments, and reflecting surface elements 22s, which are different in curvature from the aforementioned reference surface are assigned to those segments. Those reflecting surface elements 22s' reflect the output light of the discharge bulb downwardly, and reflects it horizontally in a diffuse mode.

Similarly as in the case of the reflecting surface elements 22s forming the reflecting surface region 22A, in the case of the reflecting surface elements 22s, forming the reflecting surface region 22B, its vertical section is of a parabola having a focal distance f. On the other hand, as shown in FIG. 4 which is a sectional view taken along line IV-IV in FIG. 1, in order to downwardly deflect the light reflected from the reflecting surface elements 22s, forming the reflecting surface region 22B, as shown in FIG. 5(a) the parabolic axis Ax' of the reflecting surface region 22B is extended downwardly with respect to the parabolic axis Ax of the reflecting surface region 22B (which is in parallel with the optical axis Ax of the reflector).

As was described above, the light reflected from the reflecting surface region 22A which is a substantially upper half of the reflector 16 with respect to the optical axis Ax of the latter 16, forms the sub light distribution pattern P, while the light reflected from the reflecting surface region 22B located below the optical axis Ax forms the wide diffusion distribution pattern Pw in a part of the sub light distribution pattern P near the vehicle which has a horizontal diffusion angle larger than the maximum horizontal diffusion angle thereof. Hence, with the sub light distribution pattern, the driver is able to ensure the traveling safety of the vehicle moving forwardly, and to find a walking person quickly who may appear in front of the vehicle suddenly from side. Thus, the auxiliary functions of the sub light distribution pattern can be fully utilized.

Therefore, the sub light distribution pattern forming vehicle headlight with the discharge bulb of the invention is high in lamp efficiency and in the driving safety of a vehicle at night.

Furthermore, the aforementioned wide diffusion distribution pattern Pw is formed by the utilization of light reflected from the reflecting surface region 22B which is located below the optical axis Ax. This feature provides the following effects and merits:

That is, as shown in FIG. 6, metal iodide 18c is deposited on the lower portion of the inner wall of a ballshaped section 18b which forms the discharge chamber of the discharge bulb 18. Hence, the light advancing downwardly i from the light emitting section 18a which is made up of a pair of electrode rods, is colored yellow. Hence, the light reflected from the reflecting surface region 22 which is located below the optical axis Ax of the reflector is substantially colored yellow. With the yellowish wide diffusion distribution pattern Pw yellow thus formed, in the traveling of the vehicle at night even in bad weather such as foggy weather, the front field of vision of the vehicle is sufficiently clear.

The reflecting surface region 22B is made up of a plurality of reflecting surface elements 22s, which reflect the output light of the discharge bulb 18 downwardly and reflect it horizontally in a diffusion mode. Hence, the aforementioned wide diffusion distribution pattern Pw can be formed with ease.

In the above-described embodiment, in order to downwardly deflect the light reflected from the reflecting surface elements 22s, forming the reflecting surface region 22B, as shown in FIG. 5(a) the parabolic axis Ax, of the reflecting surface region 22B extends downwardly with respect to the parabolic axis Ax of the reflecting surface region 22A. However, instead of this fact, as shown in FIG. 5(b), the parabolic axis Ax' of the reflecting surface region 22B may be laid below the parabolic axis Ax of the reflecting surface region 22A. In this connection, if the parabolic focal position of the reflecting surface region 22B is shifted behind the parabolic focal position of the reflecting surface region 22A, then the angle of downward deflection of the light thus reflected can be increased. Alternatively, as shown in FIG. 5(c), the parabolic focal length f2 of the reflecting surface region 22B may be longer than the parabolic focal length fl of the reflecting surface region 22A. In addition, the arrangements of FIGS. 5(a), 5(b) and 5(c) may be suitably combined together in practical use.

In the above-described embodiment, the pair of legs 20bl and 20b2 of the shade 20 form the pair of shades SB1 and SB2 on the reflecting surface 22, so that the sub light distribution pattern P forming reflecting surface region 22A, and the wide diffusion distribution pattern Pw forming reflecting surface region 22B are distinguished from each other; however, the same effect can be obtained as follows: That is, as shown in FIG. 7, a pair of black stripes (beltshaped films) 18fl and 1M are formed on the right and left sides of the outer tube 18e of the discharge bulb 18.

As was described above, in the reflecting surface 22 of the reflector 16, the sub light distribution pattern forming reflecting surface region 22A is divided into a plurality of segments. In this case, in view of the design, sometimes it is desirable that, as shown in FIG. 8, the upper and lower border line Ll located above the oblique cut line forming region is provided above the upper and lower border line in the reflecting surface region 22A shown in FIG. 1.

In this case, it is not desirable that the upper and lower border line L2 located between the horizontal cut line forming region 22Aa and the region 22Ab located above the former 22Aa is positioned at the same level as the upper and lower border line L1 as indicated by the two-dot chain line in FIG. 8; instead, in order to improve the lamp distribution, it is desirable that the upper and lower border line L2 is left positioned as indicated by the solid line in FIG. 8.

That is, as shown in FIG. 9, the distribution pattern PBa formed by light reflected from the horizontal cut line forming region 22Aa is to irradiate objects which are located far away from the vehicle, and therefore the pattern PBa is smaller in horizontal diffusion angle than the distribution pattern PBb formed by light reflected from the region 22Ab. It is assumed that the upper and lower border line L2 is set as indicated by the two-dot chain line instead of the solid line in FIG. 8. In this case, as indicated by the two-dot chain line in FIG. 9, the distribution pattern PBa, which is relatively small in horizontal diffusion angle and bright, is extended near to the vehicle while the distribution pattern PBa, which is relatively large in horizontal diffusion angle, is not extended far away from the vehicle. Hence, the sub light distribution pattern is formed which is such that light beams are liable to be collected on the surface of the road in front of the vehicle, and it is rather difficult to observe objects which are located far away from the vehicle on the right side.

Hence, it is desirable that, as shown in FIG. 8, the upper and lower border line L2 is located slightly below the level which divides the space between the optical axis Ax of the reflector 16 and the upper edge of the reflecting surface 22 into two parts.

Claims

1. A vehicle headlight which comprises a discharge bulb, and a reflector having a reflecting surface for reflecting an output light of the discharge bulb forwardly, and forms a sub light distribution pattern having an oblique cut line and a horizontal cut line, wherein of the reflecting surface, a first reflecting surface region which is a substantially upper half thereof with respect to the optical axis of the reflector, is so designed as to form the sub light distribution pattern with the aid of light reflected from the first reflecting surface region, and of the reflecting surface, a second reflecting surface region which is located below the optical axis of the reflector reflects the output light of the discharge bulb downwardly in a deflection mode and reflect the output light of the discharge bulb horizontally in a diffusion mode, so that light reflected from the second reflecting surface region forms in a part of the sub light distribution pattern near a vehicle a wide diffusion sub light distribution pattern which has a horizontal diffusion angle larger than the maximum horizontal diffusion angle of the sub light distribution pattern.

2. The vehicle headlight according to claim 1, wherein the second reflecting surface region comprises a 16- plurality of reflecting surface elements.

3. The vehicle headlight as claimed in any one of the preceding claims, wherein a shade is provided near the discharge bulb, the shade comprising a front end portion adapted to intercept light emitted forwardly from the discharge bulb, and a pair of legs through which the front end portion is secured to the reflector, and the upper edges of the pair of legs form the oblique cut line and the horizontal cut line, and the second reflecting surface region is a reflecting surface region which is located between the shades of the pair of legs.

4. The vehicle headlight as claimed in any one of the preceding claims, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic axis of the second reflecting surface region is directed downwardly with respect to the parabolic axis of the first reflecting surface region.

5. The vehicle headlight as claimed in any one of the preceding claims, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic axis of the second reflecting surface region is located below the parabolic axis of the first reflecting surface region.

6. The vehicle headlight as claimed in any one of the preceding claims, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic focal length of the second reflecting surface region is longer than the parabolic focal length of the first reflecting surface region.

7. A reflector for a vehicle headlight having a reflecting surface for reflecting an output light of a discharge bulb forwardly, and forms a sub light distribution pattern having an oblique cut line and a horizontal cut line, wherein of the reflecting surface, a first reflecting surface region which is a substantially upper half thereof with respect to the optical axis of the reflector, is so designed as to form the sub light distribution pattern with the aid of light reflected from the first reflecting surface region, and of the reflecting surface, a second reflecting surface region which is located below the optical -18 axis of the reflector reflects the output light of the discharge bulb downwardly in a deflection mode and reflect the output light of the discharge bulb horizontally in a diffusion mode, so that light reflected from the second reflecting surface region forms in a part of the sub light distribution pattern near a vehicle a wide diffusion sub light distribution pattern which has a horizontal diffusion angle larger than the maximum horizontal diffusion angle of the sub light distribution pattern.

8. The reflector according to claim 7, wherein the second reflecting surface region comprises a plurality of reflecting surface elements.

9. The reflector according to claim 7 or 8, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic axis of the second reflecting surface region is directed downwardly with respect to the parabolic axis of the first reflecting surface region.

10. The reflector according to claim 7, 8 or 9, sections oz the -=i-sz and second surface recions are parabe-l-i--, and the oara-'-cl-c axiss of the second sur-face region is located below the parabolic axis of the first -lect- ng su r'ace region.

!I. The reflector according to clain, 7-9 or 10, where-in first and second sections of the surface- rec-icns are parabclic, and the parabolic 'Local length of z'n=- ce r=g-;cn is longer than the pa-ra'--ol-ic focal lencz, of the fi-rst reflecting surface region.

A vehicle headlight, substantially as described with reference to the accompanying drawings.

10. The reflector according to claim 7, 8 or 9, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic axis of the second reflecting surface region is located below the parabolic axis of the first reflecting surface region.

11. The reflector according to claim 7-9 or 10, wherein the vertical sections of the first and second reflecting surface regions are parabolic, and the parabolic focal length of the second reflecting surface region is longer than the parabolic focal length of the first reflecting surface region.

2- k Amendments to the claims have been fil ed as follows CL A i ill! S 1 A vehicle headlicht co,-,,z-ises a discharge a- output light c the d-;--z'-arce bulb forwardly, f cat:er- hav-lnc an oblicue refle-c- frazzi the rst re -f lect ing surface tne a- recion, and of the rei'lec:t-;r.g suricace, a second re.lec:t-fr.c: surface rea-;or, which is locate,-' below the =tical discha=ge bulb downwardly in a defilect.Lon mode and reflects ight of the d-ischarge bulb hor-Jzontally in a tLe- c,tput 1 L diffusion mode, so that i-icht reflected: from the second re-lecting surface rezion in a part cE the sub licht oattern, which has a horizontal p-c:ez than the ma.<m,,in, l.orzont;-! ancle c.; plurality of reflecting surface elements.

4. The vehicle headlight as claimed in any one of the preceding claims, wherein the vertical sections of the first and second reflec ting surface regions are parabolic, and the parabolic axis of the second reflecting surface region is directed downwardly with respect to the parabolic axis of the first reflecting surface region.

5. The vehicle headlight as claimed in any one of the preceding claims, wherein the vertical sections of the first and second reflectinc surface regions are parabolic, and the parabolic axis of the second reflecting surface recion is located below the Darabolic axis of the first reflecting surface region.

The vehicle headlicht as in any one cf- ina claizis, wherein the vertical sections of the first and second surface regions are parabolic, and the parabolic focal length of the second reflecting surface region is longer than the parabolic focal length of the first reflecting surface region.

7. A reflector for a vehicle headlight having a reflecting surface for reflecting an output light of a discharge bulb 'forwardly, and-fc=minga sub light distribution having an oblique cut line and a horizontal cut line, of the reflecting surface, a first reflecting surface recion which is a substantially upper half thereof to the optical axis of the re-f-lector, is so to form, the sub light distribution pattern with cf the reflecting surface, a second reflecting surf-ace rezion which is located belo.,,; the axis of the reflector reflects the output light cl' the discharge bulb downwardly in a deflection mode and reflects the cutout light of the discharge bulb he=izantally in a "lected from the second diffusion mode, so that!Lght re reflecting surface region fori-ns in a part oil the sub light distribution patter-n near a a wide diffusion sub ca 1 -cnz distributio,- pattern wh ich has a hc--izontal di.1 L -- acl=larger than the max-Lmun, horizontal diffusion ancle c:the sub light d-; stribut-icn pattern.

8. The refflector accordina to claim 7, wherein the second reflecting surface region comprises a plurality of reflecting surface elements.

9. The reflector according to claim 7 or 8, wherein L.he vertical sections of the first and second reflecting surface regions are parabolic, and Electing surface the parabolic axis of the second reL rezion is directed downwardly with respect to the parabolic axis ol the first re..Ilec-t--fnc surface regicn.